Dissociated cell cultures of dopaminergic neurons from embryonic rat mesencephalon were grown in completely defined serum-free medium. When exposed to increased levels of extracellular potassium, these cultures are damaged mainly via NMDA-receptors. Reasoning that cells in vivo could be exposed to an excessive concentration of extracellular K+ during ischemia or anoxia, we investigated the sequence of events involved in neurotoxicity following exposure to K+ and compared these to the events following exposure to NMDA. The damage following exposure to K+ is blocked by MK-801 (2.5muM), indicating a role for NMDA receptor. Inhibitor of non-NMDA-receptor CNQX (2.5, 5, 10muM) do not protect neurons high K+-induced damage. The damage does not occur in Ca++-free media. Calmodulin antagonist W-5 (150-200muM) completely protects neurons from that type of damage. If an inhibitor of Calmodulin dependent Protein Kinase II, KN-62, (1muM) presents in the media, about 60-70% neurons survive. At the same time if an inhibitor of Calmodulin dependent Phosphotase Calcineurin, Cyclosporin A, (1muM) presents in the media, only 30-40% neurons survive. Our data demonstrates that from mentioned above inhibitors in the case of NMDA toxicity induced by high concentration of NMDA (100muM) only inhibitor of NMDA receptor MK-801 protects neurons exposed from damage. However the damage of neurons by lower concentration of NMDA (25muM) can be blocked completely by W-5 (10muM) and Cyclosporin A (1muM). The damage of neurons by 50muM NMDA can be blocked significantly by the same inhibitors. Inhibitors of Calmodulin dependent PK II; KN-62 (5fM), deteriorate survival of neurons exposed to NMDA.